Ectopic matrix metalloproteinase-9 expression in human brain tumor cells enhances oncolytic HSV vector infection

Immune landscape and response to oncolytic virus-based immunotherapy

Oncolytic virus (OV)-based immunotherapy has emerged as a promising strategy for cancer treatment, offering a unique potential to selectively target malignant cells while sparing normal tissues. However, the immunosuppressive nature of tumor microenvironment (TME) poses a substantial hurdle to the development of OVs as effective immunotherapeutic agents, as it restricts the activation and recruitment of immune cells. This review elucidates the potential of OV-based immunotherapy in modulating the immune landscape within the TME to overcome immune resistance and enhance antitumor immune responses. We examine the role of OVs in targeting specific immune cell populations, including dendritic cells, T cells, natural killer cells, and macrophages, and their ability to alter the TME by inhibiting angiogenesis and reducing tumor fibrosis. Additionally, we explore strategies to optimize OV-based drug delivery and improve the efficiency of OV-mediated immunotherapy. In conclusion, this review offers a concise and comprehensive synopsis of the current status and future prospects of OV-based immunotherapy, underscoring its remarkable potential as an effective immunotherapeutic agent for cancer treatment.

Agent-based computational modeling of glioblastoma predicts that stromal density is central to oncolytic virus efficacy

Oncolytic viruses (OVs) are emerging cancer immunotherapy. Despite notable successes in the treatment of some tumors, OV therapy for central nervous system cancers has failed to show efficacy. We used an ex vivo tumor model developed from human glioblastoma tissue to evaluate the infiltration of herpes simplex OV rQNestin (oHSV-1) into glioblastoma tumors. We next leveraged our data to develop a computational, model of glioblastoma dynamics that accounts for cellular interactions within the tumor. Using our computational model, we found that low stromal density was highly predictive of oHSV-1 therapeutic success, suggesting that the efficacy of oHSV-1 in glioblastoma may be determined by stromal-to-tumor cell regional density. We validated these findings in heterogenous patient samples from brain metastatic adenocarcinoma. Our integrated modeling strategy can be applied to suggest mechanisms of therapeutic responses for central nervous system cancers and to facilitate the successful translation of OVs into the clinic.

Replication and Spread of Oncolytic Herpes Simplex Virus in Solid Tumors

Oncolytic herpes simplex virus (oHSV) is a highly promising treatment for solid tumors. Intense research and development efforts have led to first-in-class approval for an oHSV for melanoma, but barriers to this promising therapy still exist that limit efficacy. The process of infection, replication and transmission of oHSV in solid tumors is key to obtaining a good lytic destruction of infected cancer cells to kill tumor cells and release tumor antigens that can prime anti-tumor efficacy. Intracellular tumor cell signaling and tumor stromal cells present multiple barriers that resist oHSV activity. Here, we provide a review focused on oncolytic HSV and the essential viral genes that allow for virus replication and spread in order to gain insight into how manipulation of these pathways can be exploited to potentiate oHSV infection and replication among tumor cells.

Simultaneous Tumor and Stroma Targeting by Oncolytic Viruses

Current cancer therapeutics often insufficiently eradicate malignant cells due to the surrounding dense tumor stroma. This multi-componential tissue consists of mainly cancer-associated fibroblasts, the (compact) extracellular matrix, tumor vasculature, and tumor-associated macrophages, which all exert crucial roles in maintaining a pro-tumoral niche. Their continuous complex interactions with tumor cells promote tumor progression and metastasis, emphasizing the challenges in tumor therapy development. Over the last decade, advances in oncolytic virotherapy have shown that oncolytic viruses (OVs) are a promising multi-faceted therapeutic platform for simultaneous tumor and stroma targeting. In addition to promoting tumor cell oncolysis and systemic anti-tumor immunity, accumulating data suggest that OVs can also directly target stromal components, facilitating OV replication and spread, as well as promoting anti-tumor activity. This review provides a comprehensive overview of the interactions between native and genetically modified OVs and the different targetable tumor stromal components, and outlines strategies to improve stroma targeting by OVs.

The enhanced efficacy of herpes simplex virus by lentivirus mediated VP22 and cytosine deaminase gene therapy against glioma

Despite the comprehensive treatment of surgery following by concurrent radiochemotherapy, the prognosis of malignant glioma remains unsatisfactory with an awful median survival time of only 12-18 months. This might be improved by the development of oncolytic herpes simplex virus. However, the biggest challenge of recombinant herpes simplex virus (rHSV) lies in their limited therapeutic efficiency in clinical trials. This study aims to enhance the efficacy of rHSV against glioma by a HSV-1 tegument protein VP22 modified cytosine deaminase/5-flurocytosine (CD/5-FC) suicide gene system. Stable glioma cell lines carrying CD or VP22-CD fusion gene were successfully obtained by lentiviral infection following Fluorescence-activated cell sorting. The lethal effect of the prodrug 5-FC was significantly increased in the transduced VP22-CD glioma cells compared to the transduced CD glioma cells. Interestingly, VP22 was found to elicit the enhanced efficacy of rHSV-1 against glioma. Furthermore, we detected a synergistic efficacy of rHSV-1 combined with lentivirus mediated VP22 and CD suicide gene therapy in the orthotopic glioma xenograft models. In conclusion, we successfully established the stable cell lines carrying VP22-CD fusion genes. The incorporation of VP22 further induced an enhanced efficacy of rHSV-1 as well as CD suicide gene therapy respectively and synthetically in vitro. Also, we demonstrated an increased therapeutic benefit of rHAV-1 by VP22 modified CD gene therapy against glioma in vivo.

GBM-Targeted oHSV Armed with Matrix Metalloproteinase 9 Enhances Anti-tumor Activity and Animal Survival

The use of mutant strains of oncolytic herpes simplex virus (oHSV) in early-phase human clinical trials for the treatment of glioblastoma multiforme (GBM) has proven safe, but limited efficacy suggests that more potent vector designs are required for effective GBM therapy. Inadequate vector performance may derive from poor intratumoral vector replication and limited spread to uninfected cells. Vector replication may be impaired by mutagenesis strategies to achieve vector safety, and intratumoral virus spread may be hampered by vector entrapment in the tumor-specific extracellular matrix (ECM) that in GBM is composed primarily of type IV collagen. In this report, we armed our previously described epidermal growth factor receptor (EGFR)vIII-targeted, neuronal microRNA-sensitive oHSV with a matrix metalloproteinase (MMP9) to improve intratumoral vector distribution. We show that vector-expressed MMP9 enhanced therapeutic efficacy and long-term animal survival in a GBM xenograft model.

Three-dimensional tumor cell cultures employed in virotherapy research

Oncolytic virotherapy constitutes an upcoming alternative treatment option for a broad spectrum of cancer entities. However, despite great research efforts, there is still only a single US Food and Drug Administration/European Medicines Agency-approved oncolytic virus available for clinical use. One reason for that is the gap between promising preclinical data and limited clinical success. Since oncolytic viruses are biological agents, they might require more realistic in vitro tumor models than common monolayer tumor cell cultures to provide meaningful predictive preclinical evaluation results. For more realistic invitro tumor models, three-dimensional tumor cell-culture systems can be employed in preclinical virotherapy research. This review provides an overview of spheroid and hydrogel tumor cell cultures, organotypic tumor-tissue slices, organotypic raft cultures, and tumor organoids utilized in the context of oncolytic virotherapy. Furthermore, we also discuss advantages, disadvantages, techniques, and difficulties of these three-dimensional tumor cell-culture systems when applied specifically in virotherapy research.

Digesting a Path Forward: The Utility of Collagenase Tumor Treatment for Improved Drug Delivery

Collagen and hyaluronan are the most abundant components of the extracellular matrix (ECM) and their overexpression in tumors is linked to increased tumor growth and metastasis. These ECM components contribute to a protective tumor microenvironment by supporting a high interstitial fluid pressure and creating a tortuous setting for the convection and diffusion of chemotherapeutic small molecules, antibodies, and nanoparticles in the tumor interstitial space. This review focuses on the research efforts to deplete extracellular collagen with collagenases to normalize the tumor microenvironment. Although collagen synthesis inhibitors are in clinical development, the use of collagenases is contentious and clinically untested in cancer patients. Pretreatment of murine tumors with collagenases increased drug uptake and diffusion 2-10-fold. This modest improvement resulted in decreased tumor growth, but the benefits of collagenase treatment are confounded by risks of toxicity from collagen breakdown in healthy tissues. In this review, we evaluate the published in vitro and in vivo benefits and limitations of collagenase treatment to improve drug delivery.

Control of Human T-Cell Leukemia Virus Type 1 (HTLV-1) Infection by Eliminating Envelope Protein-Positive Cells with Recombinant Vesicular Stomatitis Viruses Encoding HTLV-1 Primary Receptor

Human T-cell leukemia virus type 1 (HTLV-1) infection causes adult T-cell leukemia (ATL), which is frequently resistant to currently available therapies and has a very poor prognosis. To prevent the development of ATL among carriers, it is important to control HTLV-1-infected cells in infected individuals. Therefore, the establishment of novel therapies with drugs specifically targeting infected cells is urgently required. This study aimed to develop a potential therapy by generating recombinant vesicular stomatitis viruses (rVSVs) that lack an envelope glycoprotein G and instead encode an HTLV-1 receptor with human glucose transporter 1 (GLUT1), neuropilin 1 (NRP1), or heparan sulfate proteoglycans (HSPGs), including syndecan 1 (SDC1), designated VSVΔG-GL, VSVΔG-NP, or VSVΔG-SD, respectively. In an attempt to enhance the infectivity of rVSV against HTLV-1-infected cells, we also constructed rVSVs with a combination of two or three receptor genes, designated VSVΔG-GLN and VSVΔG-GLNS, respectively. The present study demonstrates VSVΔG-GL, VSVΔG-NP, VSVΔG-GLN, and VSVΔG-GLNS have tropism for HTLV-1 envelope (Env)-expressing cells. Notably, the inoculation of VSVΔG-GL or VSVΔG-NP significantly eliminated HTLV-1-infected cells under the culture conditions. Furthermore, in an HTLV-1-infected humanized mouse model, VSVΔG-NP was capable of efficiently preventing HTLV-1-induced leukocytosis in the periphery and eliminating HTLV-1-infected Env-expressing cells in the lymphoid tissues. In summary, an rVSV engineered to express HTLV-1 primary receptor, especially human NRP1, may represent a drug candidate that has potential for the development of unique virotherapy against HTLV-1 de novo infection.

IMPORTANCE Although several anti-ATL therapies are currently available, ATL is still frequently resistant to therapeutic approaches, and its prognosis remains poor. Control of HTLV-1 de novo infection or expansion of HTLV-1-infected cells in the carrier holds considerable promise for the prevention of ATL development. In this study, we developed rVSVs that specifically target and kill HTLV-1 Env-expressing cells (not ATL cells, which generally do not express Env in vivo) through replacement of the G gene with HTLV-1 receptor gene(s) in the VSV genome. Notably, an rVSV engineered to express human NRP1 controlled the number of HTLV-1-infected Env-expressing cells in vitro and in vivo, suggesting the present approach may be a promising candidate for novel anti-HTLV-1 virotherapy in HTLV-1 carriers, including as a prophylactic treatment against the development of ATL.

Neutralization of matrix metalloproteinase-9 potentially enhances oncolytic efficacy of tanapox virus for melanoma therapy

Matrix metalloproteinases (MMPs), which are involved in degradation of extracellular matrix, are critical regulators in tumor progression, metastasis and angiogenesis. Although induction of MMPs is frequently observed during the viral infection, the effect of MMPs on viral replication varies between viruses. MMP-9, for instance, is upregulated and promotes the replication of some viruses, such as herpes simplex virus, but inhibits the replication of others. Here, we report that infection with tanapox virus (TPV) promotes the expression of MMP-9 in the melanoma cells. In addition, we show that MMP-9 exerts an anti-viral effect on TPV replication and plays a protective role in TPV-infected melanoma cells in vitro. Moreover, the neutralization of MMP-9 in melanoma cells remarkably enhances the TPV infection and leads to a significant reduction in cell survival. In summary, this study contributes to understanding of the role played by MMP-9 in TPV infectivity and provides more insights for using TPV as cancer virotherapy in future studies. Since TPV has shown substantial oncolytic efficacy in promoting melanoma tumor regression in animal models, identifying mechanisms that suppress MMP-9 expression upon TPV infection can potentially improve its use as a melanoma virotherapy.

Oncolytic Virotherapy: A Contest between Apples and Oranges

Viruses can be engineered or adapted for selective propagation in neoplastic tissues and further modified for therapeutic transgene expression to enhance their antitumor potency and druggability. Oncolytic viruses (OVs) can be administered locally or intravenously and spread to a variable degree at sites of tumor growth. OV-infected tumor cells die in situ, releasing viral and tumor antigens that are phagocytosed by macrophages, transported to regional lymph nodes, and presented to antigen-reactive T cells, which proliferate before dispersing to kill uninfected tumor cells at distant sites. Several OVs are showing clinical promise, and one of them, talimogene laherparepvec (T-VEC), was recently granted marketing approval for intratumoral therapy of nonresectable metastatic melanoma. T-VEC also appears to substantially enhance clinical responsiveness to checkpoint inhibitor antibody therapy. Here, we examine the T-VEC paradigm and review some of the approaches currently being pursued to develop the next generation of OVs for both local and systemic administration, as well as for use in combination with other immunomodulatory agents.

Folate-targeting redox hyperbranched poly(amido amine)s delivering MMP-9 siRNA for cancer therapy

For effective gene delivery to breast cancer MCF-7 cells, a folate-targeting redox gene carrier was synthesized by Michael addition polymerization between 1-(2-aminoethyl)piperazine and N,N'-cystaminebisacrylamide. Folate was then conjugated through an amidation reaction. The obtained folate-modified hyperbranched poly(amido amine)s (FA-PAAs) degraded in the presence of glutathione and displayed excellent transfection efficiency in vitro. In particular, FA-PAAs showed much higher gene delivery efficiency than PEI-25k in the presence of serum, leading to an obvious decrease in MMP-9 protein expression and the apoptosis of MCF-7 cells. Moreover, FA-PAAs displayed lower cytotoxicity and better blood compatibility than PEI-25k, suggesting a potential application in gene therapy for tumors.

Oncolytic virotherapy using herpes simplex virus: how far have we come?

Oncolytic virotherapy exploits the properties of human viruses to naturally cytolysis of cancer cells. The human pathogen herpes simplex virus (HSV) has proven particularly amenable for use in oncolytic virotherapy. The relative safety of HSV coupled with extensive knowledge on how HSV interacts with the host has provided a platform for manipulating HSV to enhance the targeting and killing of human cancer cells. This has culminated in the approval of talimogene laherparepvec for the treatment of melanoma. This review focuses on the development of HSV as an oncolytic virus and where the field is likely to head in the future.

Oncolytic newcastle disease virus triggers cell death of lung cancer spheroids and is enhanced by pharmacological inhibition of autophagy

Lung cancer stem cells (CSCs) have recently been isolated from lung cancer patient samples and have been reported to be responsible for tumor initiation, treatment resistance and tumor recurrence. We have previously shown that oncolytic Newcastle disease virus (NDV), strain FMW (NDV/FMW) induces apoptosis in drug-resistant lung cancer cells. However, how NDV exerts its oncolytic effect on lung CSCs remains to be investigated. Here we show that NDV/FMW replicates in, and lyses CSC-enriched lung cancer spheroids and inhibits the 3D growth potential of lung cancer spheroid and agar colonies. We demonstrate that NDV/FMW triggers caspase-dependent apoptosis in lung cancer spheroids as shown by increased caspase-3 processing and Poly (ADP-ribose) polymerase (PARP) cleavage. Notably, NDV/FMW infection results in the degradation of microtubule-associated protein 1 light chain 3 (LC3) II and P62, two hallmarks of autophagy maturation, indicating that NDV/FMW promotes autophagy flux in lung cancer cell spheroids. This was further confirmed by the appearance of an increased number of double-membrane vesicles as detected by transmission electron microscopy. We also show that NDV/FMW promotes autophagy degradation in lung cancer spheroids via inhibition of the AKT/mTOR pathway. In addition, treatment of spheroids with the autophagy inhibitor, chloroquine increases NDV/FMW-induced cytotoxicity. Collectively, our data show that oncolytic NDV/FMW may be a potential strategy in targeting lung CSCs.

Retargeting Oncolytic Vesicular Stomatitis Virus to Human T-Cell Lymphotropic Virus Type 1-Associated Adult T-Cell Leukemia

Adult T cell leukemia/lymphoma (ATL) is an aggressive cancer of CD4/CD25(+) T lymphocytes, the etiological agent of which is human T-cell lymphotropic virus type 1 (HTLV-1). ATL is highly refractory to current therapies, making the development of new treatments a high priority. Oncolytic viruses such as vesicular stomatitis virus (VSV) are being considered as anticancer agents since they readily infect transformed cells compared to normal cells, the former appearing to exhibit defective innate immune responses. Here, we have evaluated the efficacy and safety of a recombinant VSV that has been retargeted to specifically infect and replicate in transformed CD4(+) cells. This was achieved by replacing the single VSV glycoprotein (G) with human immunodeficiency virus type 1 (HIV-1) gp160 to create a hybrid fusion protein, gp160G. The resultant virus, VSV-gp160G, was found to only target cells expressing CD4 and retained robust oncolytic activity against HTLV-1 actuated ATL cells. VSV-gp160G was further noted to be highly attenuated and did not replicate efficiently in or induce significant cell death of primary CD4(+) T cells. Accordingly, VSV-gp160G did not elicit any evidence of neurotoxicity even in severely immunocompromised animals such as NOD/Shi-scid, IL-2Rγ-c-null (NSG) mice. Importantly, VSV-gp160G effectively exerted potent oncolytic activity in patient-derived ATL transplanted into NSG mice and facilitated a significant survival benefit. Our data indicate that VSV-gp160G exerts potent oncolytic efficacy against CD4(+) malignant cells and either alone or in conjunction with established therapies may provide an effective treatment in patients displaying ATL.

IMPORTANCE

Adult T cell leukemia (ATL) is a serious form of cancer with a high mortality rate. HTLV-1 infection is the etiological agent of ATL and, unfortunately, most patients succumb to the disease within a few years. Current treatment options have failed to significantly improve survival rate. In this study, we developed a recombinant strain of vesicular stomatitis virus (VSV) that specifically targets transformed CD4(+) T cells through replacement of the G protein of VSV with a hybrid fusion protein, combining domains from gp160 of HIV-1 and VSV-G. This modification eliminated the normally broad tropism of VSV and restricted infection to primarily the transformed CD4(+) cell population. This effect greatly reduced neurotoxic risk associated with VSV infection while still allowing VSV to effectively target ATL cells.

Combinatorial strategies for oncolytic herpes simplex virus therapy of brain tumors

Oncolytic viruses, such as the oncolytic herpes simplex virus (oHSV), are an exciting new therapeutic strategy for cancer as they are replication competent in tumor cells but not normal cells. In order to engender herpes simplex virus with oncolytic activity and make it safe for clinical application, mutations are engineered into the virus. Glioblastoma multiforme (GBM) is the most common and deadly primary brain tumor in adults. Despite many advances in therapy, overall survival has not been substantially improved over the last several decades. A number of different oHSVs have been tested as monotherapy in early-phase clinical trials for GBM and have demonstrated safety and anecdotal evidence of efficacy. However, strategies to improve efficacy are likely to be necessary to successfully treat GBM. Cancer treatment usually involves multimodal approaches, so the standard of care for GBM includes surgery, radiotherapy and chemotherapy. In preclinical GBM models, combinations of oHSV with other types of therapy have exhibited markedly improved activity over individual treatments alone. In this review, we will discuss the various combination strategies that have been employed with oHSV, including chemotherapy, small-molecule inhibitors, antiangiogenic agents, radiotherapy and expression of therapeutic transgenes. Effective combinations, especially synergistic ones, are clinically important not just for improved efficacy but also to permit lower and less-toxic doses and potentially overcome resistance.

Therapeutic potential of oncolytic Newcastle disease virus: a critical review

Newcastle disease virus (NDV) features a natural preference for replication in many tumor cells compared with normal cells. The observed antitumor effect of NDV appears to be a result of both selective killing of tumor cells and induction of immune responses. Genetic manipulations to change viral tropism and arming the virus with genes encoding for cytokines improved the oncolytic capacity of NDV. Several intracellular proteins in tumor cells, including antiapoptotic proteins (Livin) and oncogenic proteins (H-Ras), are relevant for the oncolytic activity of NDV. Defects in the interferon system, found in some tumor cells, also contribute to the oncolytic selectivity of NDV. Notwithstanding, NDV displays effective oncolytic activity in many tumor types, despite having intact interferon signaling. Taken together, several cellular systems appear to dictate the selective oncolytic activity of NDV. Some barriers, such as neutralizing antibodies elicited during NDV treatment and the extracellular matrix in tumor tissue appear to interfere with spread of NDV and reduce oncolysis. To further understand the oncolytic activity of NDV, we compared two NDV strains, ie, an attenuated virus (NDV-HUJ) and a pathogenic virus (NDV-MTH-68/H). Significant differences in amino acid sequence were noted in several viral proteins, including the fusion precursor (F0) glycoprotein, an important determinant of replication and pathogenicity. However, no difference in the oncolytic activity of the two strains was noted using human tumor tissues maintained as organ cultures or in mouse tumor models. To optimize virotherapy in clinical trials, we describe here a unique organ culture methodology, using a biopsy taken from a patient’s tumor before treatment for ex vivo infection with NDV to determine the oncolytic potential on an individual basis. In conclusion, oncolytic NDV is an excellent candidate for cancer therapy, but more knowledge is needed to ensure success in clinical trials.

Targeting the hallmarks of cancer with therapy-induced endoplasmic reticulum (ER) stress

The endoplasmic reticulum (ER) is at the center of a number of vital cellular processes such as cell growth, death, and differentiation, crosstalk with immune or stromal cells, and maintenance of proteostasis or homeostasis, and ER functions have implications for various pathologies including cancer. Recently, a number of major hallmarks of cancer have been delineated that are expected to facilitate the development of anticancer therapies. However, therapeutic induction of ER stress as a strategy to broadly target multiple hallmarks of cancer has been seldom discussed despite the fact that several primary or secondary ER stress-inducing therapies have been found to exhibit positive clinical activity in cancer patients. In the present review we provide a brief historical overview of the major discoveries and milestones in the field of ER stress biology with important implications for anticancer therapy. Furthermore, we comprehensively discuss possible strategies enabling the targeting of multiple hallmarks of cancer with therapy-induced ER stress.

New Methods in Tissue Engineering: Improved Models for Viral Infection

New insights in the study of virus and host biology in the context of viral infection are made possible by the development of model systems that faithfully recapitulate the in vivo viral life cycle. Standard tissue culture models lack critical emergent properties driven by cellular organization and in vivo-like function, whereas animal models suffer from limited susceptibility to relevant human viruses and make it difficult to perform detailed molecular manipulation and analysis. Tissue engineering techniques may enable virologists to create infection models that combine the facile manipulation and readouts of tissue culture with the virus-relevant complexity of animal models. Here, we review the state of the art in tissue engineering and describe how tissue engineering techniques may alleviate some common shortcomings of existing models of viral infection, with a particular emphasis on hepatotropic viruses. We then discuss possible future applications of tissue engineering to virology, including current challenges and potential solutions.

Use of miRNA response sequences to block off-target replication and increase the safety of an unattenuated, glioblastoma-targeted oncolytic HSV

Glioblastoma multiforme (GBM) is an aggressive brain cancer for which there is no effective treatment. Oncolytic HSV vectors (oHSVs) are attenuated lytic viruses that have shown promise in the treatment of human GBM models in animals, but their efficacy in early phase patient trials has been limited. Instead of attenuating the virus with mutations in virulence genes, we engineered four copies of the recognition sequence for miR-124 into the 3'UTR of the essential ICP4 gene to protect healthy tissue against lytic virus replication; miR-124 is expressed in neurons but not in glioblastoma cells. Following intracranial inoculation into nude mice, the miR-124-sensitive vector failed to replicate or show overt signs of pathogenesis. To address the concern that this safety feature may reduce oncolytic activity, we inserted the miR-124 response elements into an unattenuated, human receptor (EGFR/EGFRvIII)-specific HSV vector. We found that miR-124 sensitivity did not cause a loss of treatment efficiency in an orthotopic model of primary human GBM in nude mice. These results demonstrate that engineered miR-124 responsiveness can eliminate off-target replication by unattenuated oHSV without compromising oncolytic activity, thereby providing increased safety.

Choindroitinase ABC I-mediated enhancement of oncolytic virus spread and anti tumor efficacy: a mathematical model

Oncolytic viruses are genetically engineered viruses that are designed to kill cancer cells while doing minimal damage to normal healthy tissue. After being injected into a tumor, they infect cancer cells, multiply inside them, and when a cancer cell is killed they move on to spread and infect other cancer cells. Chondroitinase ABC (Chase-ABC) is a bacterial enzyme that can remove a major glioma ECM component, chondroitin sulfate glycosoamino glycans from proteoglycans without any deleterious effects in vivo. It has been shown that Chase-ABC treatment is able to promote the spread of the viruses, increasing the efficacy of the viral treatment. In this paper we develop a mathematical model to investigate the effect of the Chase-ABC on the treatment of glioma by oncolytic viruses (OV). We show that the model's predictions agree with experimental results for a spherical glioma. We then use the model to test various treatment options in the heterogeneous microenvironment of the brain. The model predicts that separate injections of OV, one into the center of the tumor and another outside the tumor will result in better outcome than if the total injection is outside the tumor. In particular, the injection of the ECM-degrading enzyme (Chase-ABC) on the periphery of the main tumor core need to be administered in an optimal strategy in order to infect and eradicate the infiltrating glioma cells outside the tumor core in addition to proliferative cells in the bulk of tumor core. The model also predicts that the size of tumor satellites and distance between the primary tumor and multifocal/satellite lesions may be an important factor for the efficacy of the viral therapy with Chase treatment.

Heat-generating iron oxide nanocubes: subtle "destructurators" of the tumoral microenvironment

Several studies propose nanoparticles for tumor treatment, yet little is known about the fate of nanoparticles and intimate interactions with the heterogeneous and ever-evolving tumor environment. The latter, rich in extracellular matrix, is responsible for poor penetration of therapeutics and represents a paramount issue in cancer therapy. Hence new strategies start aiming to modulate the neoplastic stroma. From this perspective, we assessed the efficacy of 19 nm PEG-coated iron oxide nanocubes with optimized magnetic properties to mediate mild tumor magnetic hyperthermia treatment. After injection of a low dose of nanocubes (700 μg of iron) into epidermoid carcinoma xenografts in mice, we monitored the effect of heating nanocubes on tumor environment. In comparison with the long-term fate after intravenous administration, we investigated spatiotemporal patterns of nanocube distribution, evaluated the evolution of cubes magnetic properties, and examined nanoparticle clearance and degradation processes. While inside tumors nanocubes retained their magnetic properties and heating capacity throughout the treatment due to a mainly interstitial extracellular location, the particles became inefficient heaters after cell internalization and transfer to spleen and liver. Our multiscale analysis reveals that collagen-rich tumor extracellular matrix confines the majority of nanocubes. However, nanocube-mediated hyperthermia has the potential to "destructure" this matrix and improve nanoparticle and drug penetration into neoplastic tissue. This study provides insight into dynamic interactions between nanoparticles and tumor components under physical stimulation and suggests that nanoparticle-mediated hyperthermia could be used to locally modify tumor stroma and thus improve drug penetration.

Oncolytic virotherapy of canine and feline cancer

Cancer is the leading cause of disease-related death in companion animals such as dogs and cats. Despite recent progress in the diagnosis and treatment of advanced canine and feline cancer, overall patient treatment outcome has not been substantially improved. Virotherapy using oncolytic viruses is one promising new strategy for cancer therapy. Oncolytic viruses (OVs) preferentially infect and lyse cancer cells, without causing excessive damage to surrounding healthy tissue, and initiate tumor-specific immunity. The current review describes the use of different oncolytic viruses for cancer therapy and their application to canine and feline cancer.

Tumor Restrictions to Oncolytic Virus

Oncolytic virotherapy has advanced since the days of its conception but therapeutic efficacy in the clinics does not seem to reach the same level as in animal models. One reason is premature oncolytic virus clearance in humans, which is a reasonable assumption considering the immune-stimulating nature of the oncolytic agents. However, several studies are beginning to reveal layers of restriction to oncolytic virotherapy that are present before an adaptive neutralizing immune response. Some of these barriers are present constitutively halting infection before it even begins, whereas others are raised by minute cues triggered by virus infection. Indeed, we and others have noticed that delivering viruses to tumors may not be the biggest obstacle to successful therapy, but instead the physical make-up of the tumor and its capacity to mount antiviral defenses seem to be the most important efficacy determinants. In this review, we summarize the constitutive and innate barriers to oncolytic virotherapy and discuss strategies to overcome them.

Calpain-dependent clearance of the autophagy protein p62/SQSTM1 is a contributor to ΔPK oncolytic activity in melanoma

Oncolytic virotherapy is a promising strategy to reduce tumor burden through selective virus replication in rapidly proliferating cells. However, the lysis of slowly replicating cancer stem cells (CSC), which maintain neoplastic clonality, is relatively modest and the potential contribution of programmed cell death (PCD) pathways to oncolytic activity is still poorly understood. We show that the oncolytic virus ΔPK lyses CSC-enriched breast cancer and melanoma 3D spheroid cultures at low titers (0.1pfu/cell) and without resistance development and it inhibits the 3D growth potential (spheroids and agarose colonies) of melanoma and breast cancer cells. ΔPK induces calpain activation in both melanoma and breast cancer 3D cultures as determined by the loss of the p28 regulatory subunit, and 3D growth is restored by treatment with the calpain inhibitor PD150606. In melanoma, ΔPK infection also induces LC3-II accumulation and p62/SQSTM1 clearance, both markers of autophagy, and 3D growth is restored by treatment with the autophagy inhibitor chloroquine (CQ). However, expression of the autophagy-required protein Atg5 is not altered and CQ does not restore p62/SQSTM1 expression, suggesting that the CQ effect may be autophagy-independent. PD150606 restores expression of p62/SQSTM1 in ΔPK infected melanoma cultures, suggesting that calpain activation induces anti-tumor activity through p62/SQSTM1 clearance.

The potential application of a transcriptionally regulated oncolytic herpes simplex virus for human cancer therapy

BACKGROUND

Emerging studies have shown the potential benefit of arming oncolytic viruses with therapeutic genes. However, most of these therapeutic genes are placed under the regulation of ubiquitous viral promoters. Our goal is to generate a safer yet potent oncolytic herpes simplex virus type-1 (HSV-1) for cancer therapy.

METHODS

Using bacterial artificial chromosome (BAC) recombineering, a cell cycle-regulatable luciferase transgene cassette was replaced with the infected cell protein 6 (ICP6) coding region (encoded for UL39 or large subunit of ribonucleotide reductase) of the HSV-1 genome. These recombinant viruses, YE-PC8, were further tested for its proliferation-dependent luciferase gene expression.

RESULTS

The ability of YE-PC8 to confer proliferation-dependent transgene expression was demonstrated by injecting similar amount of viruses into the tumour-bearing region of the brain and the contralateral normal brain parenchyma of the same mouse. The results showed enhanced levels of luciferase activities in the tumour region but not in the normal brain parenchyma. Similar findings were observed in YE-PC8-infected short-term human brain patient-derived glioma cells compared with normal human astrocytes. intratumoural injection of YE-PC8 viruses resulted in 77% and 80% of tumour regression in human glioma and human hepatocellular carcinoma xenografts, respectively.

CONCLUSION

YE-PC8 viruses confer tumour selectivity in proliferating cells and may be developed further as a feasible approach to treat human cancers.

Monitoring the initial delivery of an oncolytic measles virus encoding the human sodium iodide symporter to solid tumors using contrast-enhanced computed tomography

BACKGROUND

We aimed to determine the feasibility of monitoring viral delivery and initial distribution to solid tumors using iodinated contrast agent and micro-computed tomography (CT).

METHODS

Human BxPC-3 pancreatic tumor xenografts were established in nude mice. An oncolytic measles virus with an additional transcriptional unit encoding the sodium iodide symporter (NIS), as a reporter for viral infection, was mixed with a 1:10 dilution of Omnipaque 300 (GE Healthcare, Milwaukee, WI, USA) contrast agent and injected directly into tumors. Mice were imaged with micro-CT immediately before and after injection to determine the location of contrast agent/virus mixture. Mice were imaged again on day 3 after injection with micro-single-photon emission CT/CT to determine the location of NIS-mediated (99m) TcO(4) transport.

RESULTS

A 1:10 dilution of Omnipaque had no effect on viral infectivity or cell viability in vitro and was more than adequate for CT imaging of the intratumoral injectate distribution. The volume of tumor coverage with initial CT contrast agent and the 3-day postinfection measurement of virally infected tumor volume were significantly correlated. Additionally, regions of the tumor that did not receive contrast agent from the initial injection were largely devoid of viral infection at early time points.

CONCLUSIONS

Contrast-enhanced viral delivery enables a rapid and accurate prediction of the initial viral distribution within a solid tumor. This technique should enable real-time monitoring of viral propagation from initially infected tumor regions to adjacent tumor regions.

Inhibition of Indoleamine-2,3-dioxygenase (IDO) in Glioblastoma Cells by Oncolytic Herpes Simplex Virus

Successful oncolytic virus treatment of malignant glioblastoma multiforme depends on widespread tumor-specific lytic virus replication and escape from mitigating innate immune responses to infection. Here we characterize a new HSV vector, JD0G, that is deleted for ICP0 and the joint sequences separating the unique long and short elements of the viral genome. We observed that JD0G replication was enhanced in certain glioblastoma cell lines compared to HEL cells, suggesting that a vector backbone deleted for ICP0 may be useful for treatment of glioblastoma. The innate immune response to virus infection can potentially impede oncolytic vector replication in human tumors. Indoleamine-2,3-dioxygenase (IDO) is expressed in response to interferon γ (IFNγ) and has been linked to both antiviral functions and to the immune escape of tumor cells. We observed that IFNγ treatment of human glioblastoma cells induced the expression of IDO and that this expression was quelled by infection with both wild-type and JD0G viruses. The role of IDO in inhibiting virus replication and the connection of this protein to the escape of tumor cells from immune surveillance suggest that IDO downregulation by HSV infection may enhance the oncolytic activity of vectors such as JD0G.

Incorporation of the B18R gene of vaccinia virus into an oncolytic herpes simplex virus improves antitumor activity

Interferon (IFN) antiviral defense mechanism plays a critical role in controlling virus infection. It thus represents a formidable hurdle for virotherapy. Despite the reported ability of herpes simplex virus (HSV) to counteract this defense, the duration and extent of HSV infection in vivo is still largely dictated by host's IFN activity status. Because the HSV genes that have been reported to block IFN activity mainly act intracellularly, we hypothesized that their inhibitory effect could be enhanced by exploiting a gene whose product acts extracellularly. The B18R gene from vaccinia virus encodes a secreted decoy receptor with a broad antagonizing effect against type I IFNs. We therefore cloned B18R into an HSV-1-based oncolytic virus to generate Synco-B18R. In the presence of increased IFN levels in vitro, Synco-B18R largely retained its oncolytic effect, whereas the tumor-killing ability of the parental virus, Synco-2D, was severely compromised. When injected intratumorally in vivo, Synco-B18R showed significantly greater oncolytic activity than Synco-2D. Our results suggest that incorporation of the vaccinia virus B18R gene can safely potentiate the antitumor effect of an oncolytic HSV, and that similar strategies may be useful with other types of oncolytic viruses.

Anti-angiogenic therapy increases intratumoral adenovirus distribution by inducing collagen degradation

Conditionally replicating adenoviruses (CRAd) are a promising class of gene therapy agents that can overcome already known glioblastoma (GBM) resistance mechanisms but have limited distribution upon direct intratumoral (i.t.) injection. Collagen bundles in the extracellular matrix (ECM) play an important role in inhibiting virus distribution. In fact, ECM pre-treatment with collagenases improves virus distributions to tumor cells. Matrix metalloproteinases (MMPs) are an endogenous class of collagenases secreted by tumor cells whose function can be altered by different drugs including anti-angiogenic agents, such as bevacizumab. In this study we hypothesized that up-regulation of MMP activity during antiangiogenic therapy can improve CRAd-S-pk7 distribution in GBM. We find that MMP-2 activity in human U251 GBM xenografts increases (*p=0.03) and collagen IV content decreases (*p=0.01) during vascular endothelial growth factor (VEGF-A) antibody neutralization. After proving that collagen IV inhibits CRAd-S-pk7 distribution in U251 xenografts (Spearman rho= −0.38; **p=0.003), we show that VEGF blocking antibody treatment followed by CRAd-S-pk7 i.t. injection reduces U251 tumor growth more than each individual agent alone (***p<0.0001). Our data proposes a novel approach to improve virus distribution in tumors by relying on the early effects of anti-angiogenic therapy.

Oncolytic virotherapy in veterinary medicine: current status and future prospects for canine patients

Oncolytic viruses refer to those that are able to eliminate malignancies by direct targeting and lysis of cancer cells, leaving non-cancerous tissues unharmed. Several oncolytic viruses including adenovirus strains, canine distemper virus and vaccinia virus strains have been used for canine cancer therapy in preclinical studies. However, in contrast to human studies, clinical trials with oncolytic viruses for canine cancer patients have not been reported. An 'ideal' virus has yet to be identified. This review is focused on the prospective use of oncolytic viruses in the treatment of canine tumors - a knowledge that will undoubtedly contribute to the development of oncolytic viral agents for canine cancer therapy in the future.

Chondroitinase ABC I-mediated enhancement of oncolytic virus spread and antitumor efficacy

PURPOSE

The inhibitory role of secreted chondroitin sulfate proteoglycans on oncolytic viral (OV) therapy was examined. Chondroitinase ABC (Chase-ABC) is a bacterial enzyme that can remove chondroitin sulfate glycosaminoglycans from proteoglycans without any deleterious effects in vivo. We examined the effect of Chase-ABC on OV spread and efficacy.

EXPERIMENTAL DESIGN

Three-dimensional glioma spheroids placed on cultured brain slices were utilized to evaluate OV spread. Replication-conditional OV-expressing Chase-ABC (OV-Chase) was engineered using HSQuik technology and tested for spread and efficacy in glioma spheroids. Subcutaneous and intracranial glioma xenografts were utilized to compare antitumor efficacy of OV-Chase, rHsvQ (control), and PBS. Titration of viral particles was performed from OV-treated subcutaneous tumors. Glioma invasion was assessed in collagen-embedded glioma spheroids in vitro and in intracranial tumors. All statistical tests were two sided.

RESULTS

Treatment with Chase-ABC in cultured glioma cells significantly enhanced OV spread in glioma spheroids grown on brain slices (P < 0.0001). Inoculation of subcutaneous glioma xenografts with Chase-expressing OV significantly increased viral titer (>10 times, P = 0.0008), inhibited tumor growth, and significantly increased overall animal survival (P < 0.006) compared with treatment with parental rHsvQ virus. Single OV-Chase administration in intracranial xenografts also resulted in longer median survival of animals than rHsvQ treatment (32 vs. 21 days, P < 0.018). Glioma cell migration and invasion were not increased by OV-Chase treatment.

CONCLUSIONS

We conclude that degradation of glioma extracellular matrix with OV-expressing bacterial Chase-ABC enhanced OV spread and antitumor efficacy.